ALBERT

Description: We present the first reported case of the simultaneous metallicity determination of a gamma-ray burst (GRB) host galaxy, from both afterglow absorption lines as well as strong emission-line diagnostics. Using spectroscopic and imaging observations of the afterglow and host of the long-duration Swift GRB 121024A at z  = 2.30, we give one of the most complete views of a GRB host/environment to date. We observe a strong damped Lyα absorber (DLA) with a hydrogen column density of log  $N({\rm H\,{\small I}})\,=\,21.88\pm 0.10$ , H 2 absorption in the Lyman–Werner bands (molecular fraction of log( f ) –1.4; fourth solid detection of molecular hydrogen in a GRB-DLA), the nebular emission lines Hα, Hβ, [O ii ], [O iii ] and [N ii ], as well as metal absorption lines. We find a GRB host galaxy that is highly star forming (SFR ~ 40 M  yr –1 ), with a dust-corrected metallicity along the line of sight of [Zn/H] corr  = –0.6 ± 0.2 ([O/H] ~ –0.3 from emission lines), and a depletion factor [Zn/Fe] = 0.85 ± 0.04. The molecular gas is separated by 400 km s –1 (and 1–3 kpc) from the gas that is photoexcited by the GRB. This implies a fairly massive host, in agreement with the derived stellar mass of log( M * /M ) =  $9.9^{+0.2}_{-0.3}$ . We dissect the host galaxy by characterizing its molecular component, the excited gas, and the line-emitting star-forming regions. The extinction curve for the line of sight is found to be unusually flat ( R V  ~ 15). We discuss the possibility of an anomalous grain size distributions. We furthermore discuss the different metallicity determinations from both absorption and emission lines, which gives consistent results for the line of sight to GRB 121024A.

Description: Long gamma-ray bursts (LGRBs) are associated with the death of massive stars. Their host galaxies therefore represent a unique class of objects tracing star formation across the observable Universe. Indeed, recently accumulated evidence shows that GRB hosts do not differ substantially from general population of galaxies at high ( z  〉 2) redshifts. However, it has been long recognized that the properties of z  〈 1.5 hosts, compared to general star-forming population, are unusual. To better understand the reasons for the supposed difference in LGRB hosts properties at z  〈 1.5, we obtained Very Large Telescope (VLT)/X-Shooter spectra of six hosts lying in the redshift range of 0.8 〈  z  〈 1.3. Some of these hosts have been observed before, yet we still lack well-constrained information on their characteristics such as metallicity, dust extinction and star formation rate (SFR). We search for emission lines in the VLT/X-Shooter spectra of the hosts and measure their fluxes. We perform a detailed analysis, estimating host average extinction, SFRs, metallicities and electron densities where possible. Measured quantities of our hosts are compared to a larger sample of previously observed GRB hosts at z  〈 2. SFRs and metallicities are measured for all the hosts analysed in this paper and metallicities are well determined for four hosts. The mass–metallicity relation, the fundamental metallicity relation and SFRs derived from our hosts occupy similar parameter space as other host galaxies investigated so far at the same redshift. We therefore conclude that GRB hosts in our sample support the found discrepancy between the properties of low-redshift GRB hosts and the general population of star-forming galaxies.

Description: We present the first reported case of the simultaneous metallicity determination of a gamma-ray burst (GRB) host galaxy, from both afterglow absorption lines as well as strong emission-line diagnostics. Using spectroscopic and imaging observations of the afterglow and host of the long-duration Swift GRB 121024A at z  = 2.30, we give one of the most complete views of a GRB host/environment to date. We observe a strong damped Lyα absorber (DLA) with a hydrogen column density of log  $N({\rm H\,{\small I}})\,=\,21.88\pm 0.10$ , H 2 absorption in the Lyman–Werner bands (molecular fraction of log( f ) –1.4; fourth solid detection of molecular hydrogen in a GRB-DLA), the nebular emission lines Hα, Hβ, [O ii ], [O iii ] and [N ii ], as well as metal absorption lines. We find a GRB host galaxy that is highly star forming (SFR ~ 40 M  yr –1 ), with a dust-corrected metallicity along the line of sight of [Zn/H] corr  = –0.6 ± 0.2 ([O/H] ~ –0.3 from emission lines), and a depletion factor [Zn/Fe] = 0.85 ± 0.04. The molecular gas is separated by 400 km s –1 (and 1–3 kpc) from the gas that is photoexcited by the GRB. This implies a fairly massive host, in agreement with the derived stellar mass of log( M * /M ) =  $9.9^{+0.2}_{-0.3}$ . We dissect the host galaxy by characterizing its molecular component, the excited gas, and the line-emitting star-forming regions. The extinction curve for the line of sight is found to be unusually flat ( R V  ~ 15). We discuss the possibility of an anomalous grain size distributions. We furthermore discuss the different metallicity determinations from both absorption and emission lines, which gives consistent results for the line of sight to GRB 121024A.

Description: Gamma-ray burst (GRB) 111215A was bright at X-ray and radio frequencies, but not detected in the optical or near-infrared (nIR) down to deep limits. We have observed the GRB afterglow with the Westerbork Synthesis Radio Telescope and Arcminute Microkelvin Imager at radio frequencies, with the William Herschel Telescope and Nordic Optical Telescope in the nIR/optical, and with the Chandra X-ray Observatory . We have combined our data with the Swift X-Ray Telescope monitoring, and radio and millimetre observations from the literature to perform broad-band modelling, and determined the macro- and microphysical parameters of the GRB blast wave. By combining the broad-band modelling results with our nIR upper limits we have put constraints on the extinction in the host galaxy. This is consistent with the optical extinction we have derived from the excess X-ray absorption, and higher than in other dark bursts for which similar modelling work has been performed. We also present deep imaging of the host galaxy with the Keck I telescope, Spitzer Space Telescope , and Hubble Space Telescope ( HST ), which resulted in a well-constrained photometric redshift, giving credence to the tentative spectroscopic redshift we obtained with the Keck II telescope, and estimates for the stellar mass and star formation rate of the host. Finally, our high-resolution HST images of the host galaxy show that the GRB afterglow position is offset from the brightest regions of the host galaxy, in contrast to studies of optically bright GRBs.

Description: Superluminous supernovae (SLSNe) are very bright explosions that were only discovered recently and that show a preference for occurring in faint dwarf galaxies. Understanding why stellar evolution yields different types of stellar explosions in these environments is fundamental in order to both uncover the elusive progenitors of SLSNe and to study star formation in dwarf galaxies. In this paper, we present the first results of our project to study SUperluminous Supernova Host galaxIES, focusing on the sample for which we have obtained spectroscopy. We show that SLSNe-I and SLSNe-R (hydrogen-poor) often (~50 per cent in our sample) occur in a class of galaxies that is known as Extreme Emission Line Galaxies (EELGs). The probability of this happening by chance is negligible and we therefore conclude that the extreme environmental conditions and the SLSN phenomenon are related. In contrast, SLSNe-II (hydrogen-rich) occur in more massive, more metal-rich galaxies with softer radiation fields. Therefore, if SLSNe-II constitute a uniform class, their progenitor systems are likely different from those of H-poor SLSNe. Gamma-ray bursts (GRBs) are, on average, not found in as extreme environments as H-poor SLSNe. We propose that H-poor SLSNe result from the very first stars exploding in a starburst, even earlier than GRBs. This might indicate a bottom-light initial mass function in these systems. SLSNe present a novel method of selecting candidate EELGs independent of their luminosity.

Description: In this paper, we compute rest-frame extinctions for the afterglows of a sample of Swift gamma-ray bursts (GRBs) complete in redshift. The selection criteria of the sample are based on observational high-energy parameters of the prompt emission and therefore our sample should not be biased against dusty sight-lines. It is therefore expected that our inferences hold for the general population of GRBs. Our main result is that the optical/near-infrared extinction of GRB afterglows in our sample does not follow a single distribution. 87 per cent of the events are absorbed by less than 2 mag, and 50 per cent suffer from less than 0.3–0.4 mag extinction. The remaining 13 per cent of the afterglows are highly absorbed. The true percentage of GRB afterglows showing high absorption could be even higher since a fair fraction of the events without reliable redshift measurement are probably part of this class. These events may be due to highly dusty molecular clouds/star-forming regions associated with the GRB progenitor or along the afterglow line of sight, and/or due to massive dusty host galaxies. No clear evolution in the dust extinction properties is evident within the redshift range of our sample, although the largest extinctions are at z  ~ 1.5–2, close to the expected peak of the star formation rate. Those events classified as dark are characterized, on average, by a higher extinction than typical events in the sample. A correlation between optical/near-infrared extinction and hydrogen-equivalent column density based on X-ray studies is shown, although the observed N H appears to be well in excess compared to those observed in the Local Group. Dust extinction does not seem to correlate with GRB energetics or luminosity.

Description: Abundances of galaxies at redshifts z  〉 4 are difficult to obtain from damped Lyα (DLA) systems in the sightlines of quasars (QSOs) due to the Lyα forest blanketing and the low number of high-redshift QSOs known to date. Gamma-ray bursts (GRBs) with their higher luminosity are well suited to study galaxies out to the formation of the first stars at z  〉 10. The large wavelength coverage of the X-shooter spectrograph makes it an excellent tool to study the interstellar medium of high-redshift galaxies, in particular if the redshift is not known beforehand. In this paper, we determine the properties of a GRB host at z  = 4.667 23 from absorption lines combined with X-ray and optical imaging data. This is one of the highest redshifts where a detailed analysis with medium-resolution data is possible. We measure a relatively high metallicity of [S/H] = –1.1 ± 0.2 for a galaxy at this redshift. Assuming ultraviolet pumping as origin for the fine-structure lines, the material observed is between 0.3 and 1.0 kpc from the GRB. The extinction determined by the spectral slope from X-rays to the infrared shows a moderate value of A V  = 0.13 ± 0.05 mag and relative abundances point to a warm disc extinction pattern. Low- and high-ionization as well as fine-structure lines show a complicated kinematic structure probably pointing to a merger in progress. We also detect one intervening system at z  = 2.18. GRB-DLAs have a shallower evolution of metallicity with redshift than QSO absorbers and no evolution in their H i column density or ionization fraction. GRB hosts at high redshifts seem to continue the trend of the metallicity–luminosity relation towards lower metallicities but the sample is still too small to draw a definite conclusion. While the detection of GRBs at z  〉 4 with current satellites is still difficult, they are very important for our understanding of the early epochs of star and galaxy formation.

Description: The quasar Q0918+1636 ( z  = 3.07) has two intervening high-metallicity Damped Lyman α Absorbers (DLAs) along the line of sight, at redshifts of z  = 2.412 and 2.583. The z  = 2.583 DLA is located at a large impact parameter of 16.2 kpc, and despite this large impact parameter it has a very high metallicity (consistent with solar), a substantial fraction of H 2 molecules and it is dusty as inferred from the reddened spectrum of the background QSO. The z  = 2.412 DLA has a metallicity of [M/H] = –0.6 (based on Zn ii and Si ii ). In this paper we present new observations of this interesting sightline consisting of deep multiband imaging and further VLT spectroscopy. By fitting stellar population synthesis models to the photometric Spectral Energy Distribution we constrain the physical properties of the z  = 2.583 DLA galaxy, and we infer its morphology by fitting a Sérsic model to its surface brightness profile. We find it to be a relatively massive ( M * 10 10 M ), strongly star-forming (SFR 30 M  yr –1 ), dusty ( E ( B  –  V ) = 0.4) galaxy with a disc-like morphology. We detect strong emission lines from the z  = 2.583 DLA ([O ii ] 3727, [O iii ] 4960, 5007, Hβ and Hα, albeit at low signal-to-noise ratio except for the [O iii ] 5007 line). The metallicity derived from the emission lines is consistent with the absorption metallicity (12 + log (O/H) = 8.8 ± 0.2). We also detect [O iii ] 5007 emission from the galaxy counterpart of the z  = 2.412 DLA at a small impact parameter (〈2 kpc). Overall our findings are consistent with the emerging picture that high-metallicity DLAs are associated with relatively luminous and massive galaxy counterparts, compared to typical DLAs.

Description: We present optical and near-infrared photometry of GRB 140606B ( z  = 0.384), and optical photometry and spectroscopy of its associated supernova (SN). The results of our modelling indicate that the bolometric properties of the SN ( M Ni  = 0.4 ± 0.2 M , M ej  = 5 ± 2 M , and E K  = 2 ± 1  x  10 52  erg) are fully consistent with the statistical averages determined for other -ray burst (GRB)-SNe. However, in terms of its -ray emission, GRB 140606B is an outlier of the Amati relation, and occupies the same region as low luminosity ( ll ) and short GRBs. The -ray emission in ll GRBs is thought to arise in some or all events from a shock breakout (SBO), rather than from a jet. The measured peak photon energy ( E p   800 keV) is close to that expected for -rays created by an SBO ( 1 MeV). Moreover, based on its position in the M V , p -L iso, plane and the E K –β plane, GRB 140606B has properties similar to both SBO-GRBs and jetted-GRBs. Additionally, we searched for correlations between the isotropic -ray emission and the bolometric properties of a sample of GRB-SNe, finding that no statistically significant correlation is present. The average kinetic energy of the sample is $\bar{E}_{\rm K} = 2.1\times 10^{52}$  erg. All of the GRB-SNe in our sample, with the exception of SN 2006aj, are within this range, which has implications for the total energy budget available to power both the relativistic and non-relativistic components in a GRB-SN event.

Description: The first observational evidence of a connection between supernovae (SNe) and gamma-ray bursts (GRBs) was found about a decade ago. Since then, only half a dozen spectroscopically confirmed associations have been discovered and XRF 1003160 associated with the type-Ic SN 20lObh is among the latest. Aims. We constrain the progenitor radius, the host-galaxy extinction, and the physical parameters of the explosion of XRF l00316D/SN 20lObh at z 0.059. We study the SN brightness and colours in the context of GRB-SNe. Methods. We began observations with the Gamma-Ray burst Optical and Near-infrared Detector (GROND) 12 hours after the GRB trigger and continued until 80 days after the burst. GROND provided excellent photometric data in six filter bands covering a wavelength range from approximately 350 to 1800 nm, significantly expanding the pre-existing data set for this event. Combining GROND and Swift data, the early broad-band spectral energy distribution (SED) is modelled with a blackbody and afterglow component attenuated by dust and gas absorption. The temperature and radius evolution of the thermal component are analysed and combined with earlier measurements available from the literature. Templates of SN 1998bw are fitted to the SN itself to directly compare the lightcurve properties. Finally, a two-component parametrized model is fitted to the quasi-bolometric light curve. which delivers physical parameters of the explosion. Results. The best-fit models to the broad-band SEDs imply moderate reddening along the line of sight through the host galaxy (A(sub v.host = 1.2 +/- 0.1 mag). Furthermore, the parameters of the blackbody component reveal a cooling envelope at an apparent initial radius of 7 x 10(exp 11) cm, which is compatible with a dense wind surrounding a Wolf-Rayet star. A multicolor comparison shows that SN 2010bh is 60 - 70% as bright as SN 1998bw. Reaching maximum brightness at 8 - 9 days after the burst in the blue bands, SN 20lObh proves to be the most rapidly evolving GRB-SNe to date. Modelling of the quasi-bolometric light curve yields M(sub Ni) = 0.21 +/- 0.03 solar M and M(sub ej) = 2.6 +/- 0.2 solar M, typical of values within the GRB-SN population. The kinetic energy is E(sub k) = (2.4 +/- 0.7) x 10(exp 52) erg, which is making this SN the second most energetic GRB-SN after SN 1998bw. Conclusions. This supernova has one of the earliest peaks ever recorded and thereafter fades more rapidly than other GRB-SNe, hypernovae, or typical type-Ic SNe. This could be explained by a thin envelope expanding at very high velocities, which is therefore unable to retain the gamma-rays that would prolong the duration of the SN event.